The present invention pertains to a control system for continuously varying the speed of a fan drive motor for a forced air indoor space heating/cooling system during startup and after shutdown of a heating/cooling cycle.
Conventional controls for forced air heating and cooling systems often provide for delayed startup of the fan drive motor at a single operating speed and delayed shutdown of the drive motor from a single operating speed after shutdown of the heat exchangers of the heating/cooling system. Conventional controls are designed to minimize unpleasant cold or hot drafts of air and to capture residual heat/cooling effect. However, changing motor speed abruptly from a deenergized or shutoff state to full speed usually generates unpleasant noise, does not preclude stratification of air in the system ductwork or in the space being heated or cooled, nor does such operation maximize the capture of residual heat/cooling effect of the system heat exchange equipment.
Control systems have been developed for forced air heating/cooling systems wherein the indoor space air circulating fan drive motor is driven at reduced speed for a period of time during startup and at a reduced speed for a period of time during the run-on or shutdown phase of the heating/cooling system operating cycle. Again, this type of control system does not minimize the stratification of warm or cold air in the ductwork or the space being heated or cooled nor does such a system maximize the capture of residual heating/cooling effect.
Prior U.S. patent applications Ser. Nos. 09/570,880 and 08/801,560 (now U.S. Pat. No. 6,070,660) assigned to the assignee of the present invention and referenced hereinabove are directed to an improved fan or blower drive motor control system and method for forced air heating/cooling systems wherein the fan drive motor speed is continuously varied during a starting phase and a shutdown phase of operation of the heating/cooling system. In one embodiment of the control system disclosed in the aforementioned patent application and patent, the system senses temperature in the airflow circuit of the heating/cooling system and prevents premature or unwanted operation of the fan drive motor. The present invention is directed to improvements in control systems of that general type. The subject matter of U.S. Pat. No. 6,070,660 issued Jun. 6, 2000 to Howard P. Byrnes, et al. is incorporated herein by reference, in its entirety.
The present invention provides an improved fan or blower drive motor control system for a forced air heating/cooling system wherein a control circuit is provided which substantially continuously varies the speed of the fan drive motor during a starting phase and a shutdown phase of operation. The control system may be easily adapted to conventional heating/cooling system controls to vary the forced air fan or blower drive motor speed in response to temperatures sensed in the heating/cooling system airflow circuit. The control system is particularly adapted for but not limited to use with permanent split capacitor or shaded pole blower or fan drive motors.
The control circuit includes an onboard power supply, an ac voltage wave crossover detector circuit and a control circuit for firing a triac to control the drive motor speed. The control system also includes a minimum speed detector circuit and a circuit which provides for continued operation of the fan drive motor at the minimum speed, if desired, or motor shutoff after reaching the minimum speed.
The control system of the present invention includes one embodiment which comprises a temperature sensor disposed in an airflow ductwork on the so-called return air side of the heating and/or cooling equipment and a temperature sensor on the downstream or so-called supply air side of the heating and/or cooling equipment.
In another embodiment, three sensors are disposed in the ductwork including the return air sensor which is disposed upstream with regard to the direction of airflow from an air heater heat exchanger, a heat sensing sensor which is disposed downstream of the air heater heat exchanger and a third sensor which is disposed downstream of an air cooling heat exchanger, such as an evaporator coil, for example. In this way a more versatile control system is provided and more accurate sensing of temperature is obtained, depending on the operating condition of the system, heating versus cooling.
The control systems of the present invention advantageously reduce energy consumption of conventional forced air heating and cooling systems, improve recovery of residual heating/cooling effect in conventional forced air heating/cooling systems, minimize stratification of air in the airflow circuit and the space being heated or cooled and reduce cold or hot air drafts during operation of the heating/cooling system. Moreover, by substantially continuously varying the fan or blower drive motor speed during startup and shutdown, noise associated with fan or blower operation is reduced and the circulation of air at a temperature other than normally sensed or preferred by occupants of an indoor space being heated or cooled is also reduced.